In an important device, system, or the like required to be constantly in operation, in order to continue to supply power to a load even when power supply from a commercial power source is interrupted due to blackout, an instantaneous power interruption, or the like (or power from a commercial power source is not or cannot be used and these cases may be hereinafter collectively referred to as “emergency situation or the like”), a UPS (Uninterruptible Power Supply) is sometimes used. The UPS has a storage battery which accumulates power to be supplied to a load in an emergency situation or the like, and a single UPS may have a plurality of storage batteries.
The storage battery used in the UPS is kept in a charged state and does not operate (discharge) in a normal situation, and operates in an emergency situation or the like so as to supply power to a load. It has been known that the storage battery degrades over time even in a non-operation state and that the degradation is accelerated generally as an ambient temperature becomes higher. Accordingly, in the case of an apparatus on which the storage battery such as the UPS is mounted, in order to prevent occurrence of the case in which the apparatus does not operate normally due to the dead battery, a failure of the storage battery or the like at the time of operation, such a method has been taken in which the state of the storage battery is monitored and the remaining battery life is predicted in consideration of the degradation caused by the ambient temperature or the service years, and the storage battery is replaced with a new storage battery before the storage battery reaches the predicted end of its service life, even when the storage battery is currently in an abnormal state as a matter of course as well as even when the storage battery is in a normal state.
However, in the simple prediction of the remaining life based on only a relation between the temperature and a degree of degradation, accuracy of the prediction of the remaining life is not so high, and accordingly, as a result of taking safety into consideration, the storage battery is replaced considerably earlier than the actual end of service life, so that the storage battery may not effectively used up, causing an inefficient state from the viewpoint of both of economical use and effective use.
As a technique for solving the above-mentioned problems, for example, Japanese Patent Application Laid-Open Publication No. 2005-26153 (Patent Document 1) discloses a storage battery monitoring system which detects a temperature T of an assembled battery composed of a plurality of storage batteries, measures a voltage E and an internal resistance R of each of the storage batteries, and determines the service life of each of the storage batteries based on these detection results and measurement results, so that the end of service life of the storage battery can be determined by further considering another element in addition to the relation between the temperature and the service life.
Moreover, Non-Patent Document 1 discloses a storage battery diagnosis device in which, in order to monitor a state of a lead storage battery used in a UPS, a cell voltage, an internal impedance, a temperature are consecutively measured, and in the measurement of the internal impedance, the internal impedance is measured at a frequency different from a frequency component of a ripple current generated from the UPS, so that an influence of normal mode noises generated from the UPS is suppressed and the measurement value of the internal impedance can be stably obtained.
Furthermore, Japanese Patent No. 5403191 (Patent Document 2) relating to the invention by the inventors of the present application discloses a storage battery state monitoring system which includes a control/power supply device detecting a current in each of the storage batteries and a slave device measuring a temperature, a voltage, and an internal resistance of each of the storage batteries, the internal resistance being measured at at least two or more kinds of frequencies, and which estimates degradation of each of the storage batteries based on at least one or more values of the temperature, the voltage, and the internal resistance measured by the slave device and a DC (direct current) resistance of each of the storage batteries obtained from a ratio between a change in a current value detected by the control/power supply device and a change in a voltage value measured by the slave device during discharging of each of the storage batteries.